1. Field of the Invention
The present invention relates generally to a drive train, and especially to a drive train for vehicles, and usually a drive train for motor vehicles.
2. Description of the Related Art
It is already known to dispose in drive trains both a hydrodynamic retarder as well as a steam-driven expansion machine—see patent specifications U.S. Pat. No. 5,121,607, U.S. Pat. No. 5,241,817 and U.S. Pat. No. 5,195,881 for example. According to these documents, a transmission contains both a hydrodynamic retarder in order to brake the vehicle in a hydrodynamic way and a steam-driven expansion machine, which is also known as an expander, in order to drive the vehicle. The expansion machine can be provided as an additional drive source in connection with a combustion engine. It is also proposed however to drive the vehicle exclusively by way of a charged screw expander in which hot combustion gases are expanded. It is further proposed to also use the expander as a brake for the vehicle.
Although different units are used in a drive train according to the mentioned specifications in order to drive the vehicle in the most energy-efficient manner, there is still room for improvements due to the rising demands made on energy efficiency. Possibilities are especially sought to better utilize the heat originating in the drive train, and especially in a motor vehicle.
JP 59 221409A describes a drive train, especially a vehicle drive train, with an engine for supplying drive power into the drive train; with a cooling circuit in which a cooling medium is revolved in order to cool the engine or an electric generator or another unit; with an expansion machine which is driven with fluid or steam as a working medium and by way of which additional drive power can be supplied to the drive train or which drives an electric generator or another unit; the cooling medium of the cooling circuit is simultaneously the working medium of the expansion machine. Reference is hereby made to the following documents regarding the further state of the art:
JP 06 088523 A
JP 57 206709 A
U.S. Pat. No. 5,176,000 A
DE 197 16 299 C1.
What is needed in the art is a drive train which is improved with respect to heat utilization over the state of the art. In addition, production, maintenance and upkeep for such a drive train shall be as cost-effective as possible and complex constructions shall be avoided to the highest possible extent.